Anti-friction bearings of the radial variety generally use ball or roller elements in prefabricated subassemblies which are installed in suitably prepared bearing seats. Very high requirements must be satisfied as to precision and shape of all structural parts which determine the bearing seat and as to care upon installation, if running precision within the .mu.m range is to be obtained for a shaft mounted in such a bearing.
For running precision within the range of 0.6 .mu.m to 1 .mu.m, complete spindle units are available which contain a plurality of ball bearings which are adapted to each other. Such units are bulky and expensive.
Highly accurate anti-friction bearings for special applications are therefore frequently manufactured as special products for the intended use. In such bearings, the rolling elements generally roll on raceways which are developed directly in the parts to be supported. For this purpose, shaft and bushing surfaces involved in running engagement must be adapted to each other with utmost precision. This approach is relatively expensive and nevertheless does not in all cases assure the desired running precision.
Running precison within the region down to a few hundredths of one .mu.m can, to be sure, be obtained with hydrostatic bearings or gas bearings. However, such bearings are unwieldy and also very expensive, due to the auxiliary pressure-fluid supply units which they require.
So-called "split-ring" or "fracture bearings" are known to provide high-load capacity in a ball bearing; they are characterized by an outer-race ring which has been fractured in order to permit reception of a maximum complement of bearing balls. In the manufacture of such a bearing, the outer ring is locally scored and then precision-ground; it is then mated to the inner-race ring, and a set of balls is selected, based on measured raceway clearance and desired ultimate bearing clearance. The outer ring is then fractured at the score, and the selected balls are introduced to complete the assembly through additional clearance afforded by transiently expanding the fractured ring. Clamping rings around the outer ring assure retention of an accurate match and continuity of the outer raceway surface at the fracture. Such bearings are not inherently free of play and must be clamped, in known manner.